#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
#include <vector>

using namespace std;

class Solution {
public:
    int waysToStep(int n)
    {
        if (n == 1) return 1;
        if (n == 2) return 2;
        if (n == 3) return 4;
        vector<long long> dp(n + 1);
        dp[0] = 0, dp[1] = 1, dp[2] = 2, dp[3] = 4;
        for (int i = 4; i <= n; i++)
        {
            dp[i] = (dp[i - 1] + dp[i - 2] + dp[i - 3]) % 1000000007;
        }
        return dp[n];
    }
};

int main()
{
    Solution s;
    cout<< s.waysToStep(5);
    return 0;
}